Problem 78 - Chemistry Matter and Change

Question

What are valence electrons? How many of a magnesium atom's 12 electrons are valence electrons?

Step-by-Step Solution

Answer

Magnesium has 2 valence electrons.

Step 1: Understanding Valence Electrons

Valence electrons are the electrons located in the outermost electron shell of an atom. These electrons are important because they participate in chemical bonding. Atoms strive to fill their outer shells to become more stable.

Step 2: Identifying Magnesium's Electron Configuration

Magnesium has an atomic number of 12, meaning it has 12 electrons. Its electron configuration is: \(1s^2 2s^2 2p^6 3s^2\). This configuration is derived by filling electron shells and orbitals from lowest to highest energy.

Step 3: Locating the Valence Electrons in Magnesium

In the electron configuration \(1s^2 2s^2 2p^6 3s^2\), the electrons in the highest energy level (the outermost shell) are in the \(3s\) orbital. Magnesium has two electrons in the \(3s\) orbital, which are its valence electrons.

Key Concepts

Electron Configuration

Electron configuration is a way to represent how electrons are distributed in an atom. Electrons are organized into shells and subshells based on their energy levels. This distribution is crucial because it determines how an atom interacts chemically with other atoms. In simple terms, the electron configuration provides a map of an atom's electrons.

• The configuration is written using numbers and letters. The numbers represent the energy levels or shells, and letters signify subshells (s, p, d, f).
• The superscripts indicate the number of electrons in each subshell.

Understanding electron configuration helps in predicting atomic behavior, especially during chemical reactions. For instance, knowing an atom's electron configuration is key to identifying its valence electrons.

Magnesium Atom

The magnesium atom is a significant element in the periodic table with the symbol Mg and atomic number 12. This atomic number represents the number of protons in the nucleus, and equivalently, the number of electrons in a neutral atom. Magnesium is crucial because of its wide use in industries and biological systems.

• Its electron configuration is given by: \(1s^2 2s^2 2p^6 3s^2\).
• Being the twelfth element, it sits in the third row of the periodic table and belongs to the alkaline earth metals.

Magnesium's electron configuration shows it has two electrons in its outermost shell, the 3s subshell. These are its valence electrons which play a central role in its chemical properties.

Chemical Bonding

Chemical bonding is the process where atoms connect to each other through their electrons. These connections are what make up molecules and compounds. The purpose of bonding is to achieve more stable electron arrangements.

Valence electrons are the key players in chemical bonding. They are the outermost electrons and are responsible for the interactions between atoms.

• Atoms can share electrons in covalent bonding.
• They can transfer electrons to form ionic bonds.

Magnesium, for example, commonly forms ionic bonds by donating its two valence electrons to achieve a stable configuration, which resembles that of the noble gas neon.

Outermost Electron Shell

The outermost electron shell, also known as the valence shell, is the highest energy level that holds electrons in an atom. The completion or partial filling of this shell dictates chemical reactivity and stability.

• Atoms tend to lose, gain, or share electrons to fill this outer shell, aiming for an electron configuration like that of a noble gas — which is considered particularly stable.
• For magnesium, the outermost shell is the third shell with its 3s subshell containing 2 electrons.

These electrons are vital for chemical reactions, as atoms will often react or bond with other atoms to fill up their outermost shell, achieving greater stability in the process.